The objective of this project is to develop a clinical test of the otolith organs using off-vertical axis rotation (OVAR). Current vestibular laboratory testing evaluates only the semicircular canals while the otolith organs are not evaluated. The importance of establishing an otolith test relates to the long term objective of improved management of patients with dizziness and disequilibrium. The specific aims of this project are: 1) To develop stimulus protocols and analysis techniques for OVAR in the dark, 2) To evaluate visual-vestibular interaction using OVAR; 3) To assess physiologic alterations of the response to OVAR in the dark; and 4) To assess the response to OVAR in selected patient groups. The OVAR testing will use a device which can deliver a prescribed rotational velocity while a patient is rotated about an axis which is tilted with respect to gravity. The device will consist of a rate-of-turn table/patient fixture which is placed on a tilt stand attached to a linear actuator. This unit will be surrounded by a cylindrical aluminum enclosure which will serve as a projection screen for visual targets during visual-vestibular interaction and adaptation studies. The OVAR stimuli will use various angles of tilt with constant velocity rotations of various amplitudes. Extraocular movements will be recorded using electro- oculography, DC coupled physiological amplifiers, and analog to digital conversion for computer disk storage and subsequent off- line analysis. A computer analysis of the eye movement data will evaluate the so-called modulation and bias components. Visual-vestibular interaction will be assessed by recording responses to OVAR in the dark, OVAR during visual fixation, and OVAR with a lighted visual surround. Physiological alterations of otolith-ocular responses will be assessed with adaptation studies using visual-vestibular conflict and with voluntary non-visual influences. Pathophysiologic alterations will be evaluated by testing persons with peripheral or central vestibular abnormalities.